Over the past several decades, the field of medical imaging has made many advances. In the 1950s, the principals of Magnetic Resonance (MR) were initially investigated. The fundamental premise of MR is that different materials resonate at different magnetic field strengths. Magnetic Resonance Imaging (MRI) was researched in the 1970s and tested clinically on patients in 1980. In 1984, MRI was approved by the Food and Drug Administration (FDA) for clinical use. Since then, this imaging modality has grown rapidly in popularity.
Computed Tomography (CT) imaging (also called CAT scanning for Computed Axial Tomography) was invented in 1972. Both gamma rays and x-rays were used in conjunction with a detector mounted on a special rotating frame to generate the image slices. Then a digital computer generates detailed cross sectional images. The original CT scan took hours to acquire a single slice of image data and more than 24 hours to reconstruct this data into a single image. Today's state-of-the-art CT systems can acquire a single image in less than a second and reconstruct the image instantly.
In the 1970s, digital imaging techniques were implemented with the first clinical use and acceptance of the CT scanner. Analog to digital converters and computers were also adapted to conventional fluoroscopic image intensifier/TV systems in the 1970s as well. The key benefits of the digital technology include the fact that digital x-ray images can be enhanced and manipulated with computers, and the fact that digital images can be sent via a network to other workstations and computer monitors so that many people can share the information and assist in the diagnosis.
Other recent developments include Positron Emission Tomography (PET), Single Photon Emission Computed Tomography (SPECT), and functional MRI (f-MRI). PET is a nuclear medicine medical imaging technique which produces a three-dimensional image or map of functional processes in the body. SPECT is a nuclear medicine tomographic imaging technique using gamma rays. It is very similar to conventional nuclear medicine planar imaging using a gamma camera. However, it is not able to provide true three-dimensional information. This information is typically presented as cross-sectional slices through the patient, but can be freely reformatted or manipulated as required. Functional magnetic resonance imaging (f-MRI) is the use of MRI to measure the hemodynamic response related to neural activity in the brain or spinal cord of humans or other animals. It is one of the most recently developed forms of neuroimaging.